SUMMARY

Brittle materials produce discontinuous chips owing to brittle failure at the shear plane before any tangible plastic flow occurs. The brittle fracture significantly influences surface integrity of the part being machined. In order to improve surface finish on machined brittle materials, ductile regime machining is being extensively studied lately. The process of machining brittle materials where material is removed by plastic flow, thus leaving a crack free surface is known as ductile-regime machining. This mode of micro-machining has been adopted based on the fact that all materials will deform plastically if the scale of deformation is very small. Ductile machining of brittle materials can produce surfaces of very high quality comparable with processes such as polishing, lapping etc. The objective of this project is to develop a robust predictive model for ductile machining of brittle materials. The model would predict the critical undeformed chip thickness (depth of cut) required to achieve ductile-regime machining. The input to the model includes tool and workpiece material properties and machining process parameters. The effect of friction in macro-scale machining is also investigated as friction coefficient has previously been shown to be sensitive to the geometry of the abrasive particle and the depth of indentation. From a micro-machining standpoint, friction coefficient is modeled to be a function of tool edge radius and undeformed chip thickness, where-in the tool edge is modeled as a sliding cylinder on a flat workpiece. The fact that the scale of machining is very small leads to a number of factors assuming significance which would otherwise be neglected. The effects of tool edge radius, grain size, grain boundaries, crystal orientation etc. are studied so as to make better predictions of forces and hence the critical undeformed chip thickness. The model is validated using a series of experiments with varying materials and cutting conditions.